1. Field of the Invention
This invention relates to a method for producing stabilized solutions of formaldehyde with methanol.
2. Description of the Related Art
Such solutions are commonly used in reactions of formaldehyde with other products, in which it is of interest to have less water than if a conventional formaldehyde-in-water solution were used and where, furthermore, the presence of methanol is desired, for example, to act as solvent for the end product obtained.
Spanish patent 447,890 discloses a process for the preparation of urea formaldehyde glues and resins, based on the preparation of said glues and or resins from methanol, by preparing a concentrated aqueous formaldehyde solution which is reacted with urea.
The process described in the above patent is characterized by the combination of the following steps:
a) methanol is catalytically oxidized in air; PA1 b) the gases from the catalytic oxidation of the methanol are condensed; PA1 c) the condensates are separated from the uncondensed gases; PA1 d) the uncondensed gases are cooled and washed in a scrubber with a cold polymerized formaldehyde solution which retains the methanol and formaldehyde contained in the gases; PA1 e) the solution obtained in step c) is distilled such that a concentrated aqueous formaldehyde solution and methanol are obtained separately; PA1 f) the solution obtained in step d) is distilled such that the methanol is recovered and the formaldehyde is fixed; PA1 g) a part of the formaldehyde solution obtained in step f) is pooled with the distilled condensate obtained in step e); PA1 h) the concentrated aqueous formaldehyde solution from step e) is mixed with urea under certain pH and temperature conditions to obtain urea-formaldehyde glues or resins.
The above described steps are effected continuously and, in a preferred embodiment, atmospheric air is aspirated at a pressure of 760 mm Hg with an appropriate compressor. The air is blown at a constant flow rate to a saturator and, therein, the air is bubbled through methanol, which is held at 50.5.degree. C. by means of a heating device. In turn, the methanol is supplied to the saturator from a reservoir at a constant rate thanks to an adequate regulation by way of a valve.
Thereafter, the mixture leaving the saturator, also at a constant methanol rate, is fed over a silver metal based catalyst held at a temperature of about 500.degree. C. such that it converts about 60% of the methanol into formaldehyde, in a conventional reaction, the corresponding hydrogen, part of which is oxidized in water by the air oxygen, being released. At the same time, a small amount of carbon dioxide is formed and practically all the air oxygen is converted during the reaction.
The gas mixture from the catalyzer is thereafter fed to the base of a scrubber receiving at the head thereof the condensates removed at the scrubber base, which are circulated by a pump and cooled by a cooler.
In the process of Spanish patent 447,890, the thus collected mixture is fed by a pump through the above mentioned remaining steps up to the preparation of the urea-formaldehyde glues and resins.